I am a law school graduate. What I offer is mere information, not to be construed as forming an attorney client relationship.
It means if there is income from that mineral lease, it will go to the designated person for her education. A few things could happen:
Designated person may not incur educational expenses/dies, etc. --> may go back to residue of estate and be dispersed among beneficiaries according to probate rules/other provisions in will (i.e. residue of estate).
Or perhaps there may not be any more money from the lease royalties which means either switching for another gift (to replace) or person goes emptyhanded.
An estate planning attorney in your state must look at the totality of circumstances, including all the provisions in the will.